1. Technical Field
The present invention is directed generally toward a contact lens and a method for making a contact lens. More specifically, the present invention is directed to a contact lens having a base curve that conforms closely to the shape of a cornea of an eye.
2. Description of Related Art
Contact lenses are becoming increasingly sophisticated in their optical characteristics. The optical characteristics of a contact lens are created by changing the nature of the front side of the contact lens. For example, a multi-focal soft contact lens that has a main carrier lens and a smaller near vision lenslet supported on the carrier lens is known. Other contact lenses change the wavefront properties of the front side of the contact lens for correcting high order aberrations. Furthermore, contact lenses may be made that are specifically tailored to an individual person's eyes.
However, a problem associated with known contact lenses is maintaining the position of a contact lens on the human eye. As a person blinks and moves his or her eyes, the contact lens will move. This movement causes the contact lens to shift on the person's eye. This shift typically causes rotation of the contact lens towards the person's nose. The result of this type of rotation is that the optical axis of the contact lens no longer matches the optical axis of the eye. Because the contact lens has specially tailored optical properties that depend on the orientation of the visual axis vis-à-vis the person's eye, the movement of the contact lens can cause the person's vision to become distorted. In addition, the shifting of the contact lens can cause discomfort in the person's eye. These two factors cause many patients to be reluctant to wear specially tailored contact lenses.
The problem of fitting a contact lens on a patient's eye so that the visual axis of the contact lens matches the patient's visual axis is known. One known method of addressing the problem is to use large diameter soft contact lenses. These contact lenses use a plastic portion outside of the visual portion, or central region, of the contact lens to orient the contact lens on the patient's eye. The plastic portion increases the amount of contact lens contacting the cornea. The plastic portion also may be formed to rest against or contact the patient's eyelid or eyelids to help maintain the contact lens in a particular orientation. However, this type of contact lens is often uncomfortable for the patient.
Another presently used method of addressing the problem of sitting contact lenses is to create a toric base curve on the contact lens to create a toric lens. Generally, the base curve is the shape of the back surface of a contact lens at any particular point or associated with any particular axis defined with respect to the contact lens. The base curve of a toric lens may be defined by two perpendicular meridians that each define a spherical curve, though the radius of curvature for each meridian is different. However, the patient must have a significant amount of astigmatism or corneal deformation for this type of lens to be a viable option. In addition, a contact lens with a toric base curve will induce astigmatism that must be negated on the front surface of the lens. Further, a patient who requires only a slightly toric lens would experience more lens rotation while wearing the contact lens and which would create more visual problems. Based on the distribution of high astigmatism in the population, this type of contact lens is only suitable for between about ten percent and about twenty percent of the population.
The problems associated with seating specially tailored contact lenses have resulted in patients with unmet optical needs. Furthermore, the business of specially tailored contact lenses is limited because only a relatively small fraction of patients can or will use these types of specially tailored contact lenses. Therefore, it would be advantageous to have an improved contact lens for seating a contact lens on the cornea of an eye.